In an electric glass melting furnace, heat is produced by Joule effect heating. Electrodes placed in the furnace are energized by a source of AC power, and current flows through the electrodes and through the melted material between the electrodes. Forehearths are connected to such furnaces to transport the molten material to forming position where the molten material is transformed into usable products. The molten material, as it flows along the forehearth, loses heat, and means must be provided to supplement this heat loss. One of the problems with providing this heat by Joule effect heating is that molten glass has a negative heat coefficient of resistance. The hotter the molten material the less electrical resistance that it provides. This can produce hot spots where more power is drawn to areas of hotter glass.
The prior art shows a number of attempts to limit and balance the power introduced between co-operating electrodes in a furnace. Rees, et al., U.S. Pat. No. 3,885,945, shows an individual transformer and controller for each pair of electrodes. Maddux, U.S. Pat. No. 3,855,412, uses a common transformer and magnetic induction coupling to achieve a balance among a group of co-operating electrodes. Williamson, U.S. Pat. No. 4,211,887, uses a single transformer with symmetrical taps on the secondary winding to achieve a distribution of voltages among electrodes.